The invention relates principally to a camera and to a visual display device.
For high-definition television, an HDQ model has been proposed for a quincuncial sequential mode. Such a mode is used both when taking pictures and upon display on cathode-ray tubes. Furthermore, all the devices operated at very high sampling frequency, for example 144 MHz; and this makes their construction difficult and their prime cost high.
In "Digest of Technical Papers" of International Conference on Consumer Electronics, June 1988, Chicago, page 60 in the article "Wide Dynamic HDTV Image Sensor with Alias Suppression", there is proposed a charge transfer sensor having a vertical quincuncial structure. The quincuncial structure relates only to the photosensitive cells and not to the spatial distribution actually sampled at the output. At each clock cycle, the signals from four elemental cells are summated to form a signal corresponding to that of a cell of larger size permitting the suppression of defects of the image.
The use of optical filters placed in front of charge transfer sensors (CCD in English-language terminology) has been proposed for the purpose of eliminating the high spatial frequencies producing folding of the spectrum beyond the half-frequency corresponding to the pitch of the sensor.
An object of the invention is digital television associating quincuncial scanning and subsampling. In order to avoid any folding of the spectrum due to the subsampling, the optical filtering of the signal is carried out. The optical filter reduces the resolution. Advantageously, the reduction of the resolution is carried out diagonally. In fact, the diminution of the resolution along the diagonals of the image causes little trouble, since it is difficult for humans to perceive this.
A further object of the invention is to provide devices for taking pictures and for visual display which are specially suitable for this type of quincuncial scanning.